Array and subtraction methods for characterising vehicle noise sub sources

摘要

Within the European Harmonoise project (1) partly funded by the EC to develop a state-of-the-art prediction model for rail and road traffic noise, there was a need to determine the power and the effective heights of vehicle sound sub sources. Microphone array methods have the potential to provide both sound exposure levels (SEL) and source heights, while single microphone subtraction methods allow a precise determination of SEL for tyre/road noise and power train noise but not effective heights. Tests were conducted at TRL to determine the accuracy of two array methods developed by TNO by comparison with the single microphone subtraction method, and also to demonstrate the arrays' ability of revealing sound sub sources on light and heavy vehicles. One array was In the form of an inverted T-shape (Acoustic Camera; shown in Figure 1b) with overall height of 1.5m. The other was a 9.5m long linear array (Syntacan; shown in Figure 1a) held in a vertical position. The single microphone subtraction method involved coast-by and cruise-by measurements at very similar vehicle speeds. Measurements were made on a surface conforming to ISO 10844, a porous surface (MARS6) and a hot rolled asphalt surface (HRA) which is commonly used on the UK road network. Test vehicles included two cars and two trucks.